If the other theory predates the concussions, the defense expert would need to show behaviors existing prior as well. If the other theory is substance abuse, etc.. after the concussions, no neuro-psychologist can get away with a failure to acknowledge the frequency of people with TBIs self medicating as a result. The same is true for isolation or failed relationships. I've got the learned treatises on my credenza.

No doubt plaintiff's (and defendant's) attorneys can usually find experts with enough "science" in their paid opinions to get past the Daubert motion to exclude their testimony - all I am saying is that winning a lawsuit is not as easy as writing a sports column that attributes a suicide to the callous and uncaring nature of a sport without any knowledge of the deceased's medical condition